巴丹吉林沙漠高大沙山背风坡植被带沉积物特征

The sediment characteristics of vegetation belt in mega-dune′s leeward slope of Badain Jaran desert

选取巴丹吉林沙漠东南部呼和吉林湖西有植被带分布的高大沙山(高差约420m),对其背风坡沙层进行采样和分析,探讨其粒度组成特征、沙层含水量变化规律及其所表达的环境信息.结果表明:高大沙山背风坡沉积物粒径较其他沙漠粗,4个4m深的剖面中部和下部出现3%～5%的较高含水量层段,植被带的发育也指示沙山较平缓处存在较高含水量层段,其中的水分会向下运移,证明该区大气降水通过入渗能够成为地下水和湖水的补给来源;上层植被带表层沉积物颗粒较粗,表明该物质是近期风沙活动的堆积物,指示高大沙山仍在移动,4个剖面平均粒径、各粒级含量的垂向变化也表明沙山在活动;4个剖面的粒度随深度呈现明显的粗细变化,反映风动力的强弱波动;海拔较高的剖面沉积物平均粒径由下向上呈增大趋势,反映沙山的活动有增强的趋势,海拔高的剖面细沙含量与中沙含量的比值大于海拔低的剖面,指示从长时间尺度看该区风动力由强变弱.

The characteristics of grain composition ,moisture content rule and their environmental information of sand layers were discussed by analyzing the samples collected from the leeward slope of mega-dune （with a height of close to 420 m） with vegetation distribution located at the southeast of Badain Jaran desert and west of Hohejilin lake. The results showed that the average diameter of sediments in mega-dune＇s leeward slope is larger than other deserts. Soil layers with water content of 3%- 5 % appeared in the middle part and lower part of four sampled sections with 4 m depths. Vegetation development also indicated soil layers with high moisture content existed at the flat part of mega-dune, and the water contained by soil layer can move down, which proved that rainfall is part of the supplement sources for lake and ground water in this region. The crude grain size of surface layer in upper vegetation belt indicated the sediments＇are accumulated by wind recently, and the mega-dune was still move, which are also verified by vertical distributions of average diameter and grain composition of four sampled sections. Grain size changed obviously with depth for four sampling sections, which reflecting the fluctuation of wind power. The average diameter increased from lower to upper for sampled sections with high elevation, which proclaimed the increasing trend of mega-dune movement. The ratios of fine sand content and medium sand content in sections with high altitude are larger than that in sections with low altitude, which indicating the wind power changed from strong to weak in a long-time scale.